Gas generator tubular charge construction and method of operation

ABSTRACT

A SOLID FUEL GAS GENERATOR SUCH AS A ROCKET ENGINE INCLUDES A COMBUSTION CHAMBER WHICH IS CLOSED AT ONE SIDE BY A COVER CONTAINING A DETONATING CAP AND HAS AN OPPOSITE CLOSED SIDE WITH A PRIMER CHARGE THEREBY. A MAIN CHARGE IN A FORM OF AN ANNULAR BURNER IS MOUNTED BETWEEN THE DETONATOR CAP AND THE PRIMER CHARGE, AND A THROTTLE RING IS INTERPOSED BETWEEN ONE END OF THE CHARGE AND THE DETONATOR CAP AND IT DEFINES PASSAGES FOR THE OUTFLOW OF GENERATED GASES PRODUCED BY THE IGNITING GASES AND THE BURNING OF THE INTERIOR OF THE MAIN CHARGE. THE THROTTLE RING PERMITS GAS TO PASS THROUGH A SCREEN DEFINED BY ONE END OF THE COVER WHICH COVERS THE DETONATING CAP. THE THROTTLING ACTION ENSURES THAT ALL OF THE GASES WHICH ARE GENERATED IN, OR DELIVERED TO, THE HOLLOW INTERIOR OF THE MAIN CHARGE DO NOT PASS DIRECTLY OUTWARDLY THROUGH THE COMBUSTION CHAMBER DISCHARGE BUT A PORTION PROCEEDS ALONG AND AROUND THE OPPOSITE END OF THE MAIN CHARGE TO INFLAME THE EXTERIOR WALL OF THE MAIN CHARGE AND TO MAINTAIN IT IGNITED.

Feb. 9, 1971 K. PAECKEL. ETAL 3,561,218

GAS GENERATOR TUBULAR CHARGE CONSTRUCTION AND METHOD OF OPERATION FiledMarch a, 1969 AT TORNE YS United States Patent 3,561,218 GAS GENERATORTUBULAR CHARGE CON- STRUCTION AND METHOD OF OPERATION Kurt Paeckel andHeinz G. Langer, Ottobrunn, Germany, assignors to Messerschmitt-BolkowGesellschaft mit beschrankter Haftung, Ottobrunn, near Munich, GermanyFiled Mar. 6, 1969, Ser. No. 804,782 Claims priority, applicationGermany, Mar. 21, 1968, P 17 51 016.6 Int. Cl. F02k 9/04 U.S. Cl. 60-20417 Claims ABSTRACT OF THE DISCLOSURE A solid fuel gas generator such asa rocket engine includes a combustion chamber which is closed at oneside by a cover containing a detonating cap and has an opposite closedside with a primer charge thereby. A main charge in a form of an annularburner is mounted between the detonator cap and the primer charge, and athrottle ring is interposed between one end of the charge and thedetonator cap and it defines passages for the outflow of generated gasesproduced by the igniting gases and the burning of the interior of themain charge. The throttle ring permits gas to pass through a screendefined by one end of the cover which covers the detonating cap. Thethrottling action ensures that all of the gases which are generated in,or delivered to, the hollow interior of the main charge do not passdirectly outwardly through the combustion chamber discharge but aportion proceeds along and around the opposite end of the main charge toinflame the exterior wall of the main charge and to maintain it ignited.

SUMMARY OF THE INVENTION This invention relates, in general, to a methodand apparatus for generating gases, and in particular, to a new anduseful device and method for the uniform ignition of both the inner andouter jacket of a solid rocket composition formed as a tubular burner ina combustion chamber such as in a rocket engine.

In solid rocket engines, it is generally known to use tubular rocketcompositions and to ignite them by means of one or more priming chargesarranged in the combustion chamber head, the igniting charge being, inturn, ignited 'by detonator caps. The ignition of solid rocketcompositions generally present some difliculties particularly for smallengines, or engines which must work at very low ambient temperatures.Special problems arise with the use of tubular burners because it isdiflicult to provide a satisfactory ignition of the outer jacket of theburner after the inner jacket is ignited, because the outer jacket doesnot come into a suflicient contact with the generated gases during andafter ignition of the priming charge thus follow the path of leastresistance and flow resistance produced by the relatively narrow gapwhich is provided between the exterior of the main charge and thesurrounding combustion chamber wall is substantially greater than theflow resistance through the interior of the charge to the discharge ofthe combustion chamber. The ignition gases which are produced by thepriming charge thus allow the path of least resistance and flowprimarily through the interior of the rocket composition directly to thecombustion chamber outlet. The small amount of ignition gases which doflow through the narrow outer annular slot of the exterior of the solidcharge cools off very rapidly due to the great heat transfer to thecombustion chamber Wall which for-ms a large surface having a greaterdensity than the charge itself.

3,561,218 Patented Feb. 9, 1971 This results in a great disadvantage inthat it provides a great ignition delay and a poor consumptionefiiciency and reduces the specific impulse of the generated gases. Inmany cases, the ignition temperatures for kindling the combustion in therange of the outer jacket of the tubular burner is not achieved at all.This can result in a pressure drop below the critical value neccessaryfor the operation of the combustion chamber and may result in thecomplete extinction of the main charge. For these reasons, the use oftubular burners is frequently forgone particularly for small rocketengines and in'solid engines which must work under the above-mentionedconditions. This is true even though they might otherwise have certainadvantages in terms of combustion characteristics and when a moreexpensive outer insulation can be forgone without risk but with the useof front and pure inner burners.

In order to avoid the difficulties of the prior art, the presentinvention provides a tubular burner which is a ranged within acombustion chamber in a manner such that the central area of the burnermay be ignited by the detonating charge and the primer charge and thegases which are generated are directed to flow outwardly from both endsof the tubular burner, one gas flow being directed around the exteriorof the main charge to maintain the ignition of the exterior and theother gas flow being directed outwardly through the engine discharge.The arrangement ensures satisfactory ignition even of the outer jacketof the tubular burner and provides a means for burning the whole chargeuniformly throughout its entire burning cycle.

In order to ensure that a portion of the gases which are generated bythe initial ignition of the interior of the charge and the primer chargegases are used to ignite the exterior wall of the main charge, theinvention provides an arrangement of a throttling between the detonatorand the charge in the path of the flow of the gases to the outlet of thecombustion chamber. The throttling increases the amount of pressureacting on this gas flow so that a portion will be diverted backwardlythrough the opposite end of the charge where it is then directed aroundthe exterior Wall of the charge to ignite and maintain ignition of thisouter wall. The throttling may be maintained over the entire combustionperiod with rocket compositions having very short combustion periods,for example, of only a few thousands or hundreds of a second. However,with engines of relatively long combustion periods, for example, ofseveral seconds or minutes, the throttling is effected only during theignition phase, that is, during the combustion of the priming charge andduring the initial phase of the combustion of the rocket composition.

According to a method of the invention, the throttling of the gascurrent produced by the igniting of the interior of the main charge, iseffected only during a predetermined operating period which issufiicient to positively ignite the outer wall of the charge and to keepthe combustion going. This length of time will depend particularly onthe type and size of the combustion chamber and on the environmentalcondition such as temperature and pressure. As a specific solution, itis suggested that a throttling element may be provided between one endof the main charge and the discharge of the combustioncharrrber. Thethrottling element may be of a combustible material or of a fusablematerial (such as plastic). Such a material should have a combustion ormelting time which corresponds to the ignition time of the outer jacketof the tubular burner. With such an arrangement, it is possible toprogressively reduce the throttling effect of the priming charge and ofthe rocket composition of the main charge during the combustion of themain charge by using a substance for the throttling element which hasthe same or higher combustion rate than the rocket composition of themain charge.

It is also possible to construct the throttling element as a ring havingan opening or flow window which is arranged around the one end of themain charge and which has a mean diameter corresponding to the meandiameter of the hollow cylindrical main charge. Such a ring may beformed of steel or other incombustible material so that it provides aconstant throttling over the entire combustion period of the maincharge.

The throttling of the gases generated by the burning of the interior ofthe main charge may be controlled in dependence on the temperature onthe gas current which is passed around the exterior of the charge in amanner such that the throttling is progressively reduced, or completelystopped, when a temperature is attained which ensures the furthercombustion on the outer wall of the main charge. To achieve this, thethrottle ring is made of a combustible material and covered over itssurface with a noncombustible insulating coat so that it will not beignited by the flow of the generated gases thereby until a temperaturesufiiciently high enough to penetrate the insulating coating isattained. The ignition may be achieved by the arrangement of theignitable temperature feelcr which is connected to the combustiblematerial of the throttle through an ignition wire which is insulated onits surface. The wire will ignite when the temperature has been reachedwhich is sufficient to ensure the ignition of the outer jacket and themaintenance of this ignition. When this occurs, the throttling isignited and the burning consumes the ring so that the ring is destroyedand the throttling effect is reduced.

A particular advantage of the invention is that a wider field ofapplication of the tubular burner is possible since a maximum combustionsurface and favorable combustion tendancies and combustion eflicienciesare attainable. A principal advantage of the tubular burner is that itscombustion rate can remain relatively low and a less expensive and lesssensitive powder can be employed for the main charge and in addition,the development risks for such a construction are very low.

Accordingly, it is an object of the invention to provide a method ofigniting and burning a hollow charge in a combustion chamber or othergas producing device which comprises igniting the central portionthereof and throttling the gases which are generated in their passage tothe discharge of the combustion chamber so as to cause the flow of aportion of these gases around the opposite end of the charge and theexterior wall of the charge in order to ignite and maintain the ignitionof the exterior wall at least for a portion of combustion period.

A further object of the invention is to provide a device for generatingthrust gases which includes a hollow solid charge mounted with one endadjacent a detonator and another end adjacent a primer charge and withthrottling means adjacent the detonator end in the path of flow from theinterior of the hollow charge to the outlet of the combustion chamberand providing a throttling elfect to divert a portion of the gases fromthe interior of the charge around the exterior wall of the charge beforeexiting through the outlet of the combustion chamber.

A further object of the invention is to provide a combustion chamberconstruction which includes a throttling member disposed between theflow path of gases from the interior of a tubular charge to the outletof the combustion chamber, the throttling member being located torequire a portion of the gases to pass around the exterior wall of thehollow charge and being made of a material, such as steel which providesa uniform throttling effect during the entire combustion period or aconsumable material which may be partially or completely consumed so asto reduce the throttling effect as combustion progresses.

A further object of the invention is to provide a gas generating devicewhich is simple in design, rugged in construction and economical tomanufacture.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated and described preferredembodiments of the invention.

In the drawings:

FIG. 1 is a partial transverse sectional view of a portion of a rocketengine combustion chamber constructed in accordance with the invention;and

FIG. 2 is an enlarged partial sectional view similar to FIG. 1 butshowing another embodiment of the throttling device.

Referring to the drawings, in particular, the invention embodied thereinin FIG. 1 comprises a gas generating device such as a rocket enginewhich includes a combustion chamber 1 in which is located a solid rocketcomposition or main charge 2. The main charge 2 is of hollow cylindricalconstruction and it is centered within the combustion chamber by meansof a centering and holding device 3. A flow passage 14 is definedbetween the interior walls 13 of the combustion chamber and the exteriorwall of the main charge 2. A priming charge 4 is disposed adjacent theinner end of the hollow main charge 2 and is slightly spaced therefromor includes passages to provide a fiowpath through this end over orthrough the priming charge 4 and through one or more passages defined inthe holding device 3.

The combustion chamber 1 includes an opposite end which is closed by acover member or housing 6 which carries a detonating charge or detonatorcap 5. The housing 6 includes an elongated tubular extension having anoutwardly extending fiange 10 which forms a flow screen having aplurality of bores 10a therethrough. The tubular end of the housing 6engages around throttle means including a throttle ring generallydesignated 7 and positions this ring between the detonating cap and theend of the hollow charge 2 adjacent a discharge or outlet 12 of thecombustion chamber.

In accordance with the invention, the throttle means are located at theend of the main charge 2 which is adjacent a gas discharge or outlet 12.The throttle means throttles the gas flow, which flows from the interiorof the charge directly to the outlet 12 and produces at least a partialbackflow in the interior of the charge and around the exterior thereofthe throttle ring 7 includes a hub portion 8 which bears against theinterior of the tubular extension of the housing 6 so that the throttlering 7 is accurately positioned against the end wall of the solid charge2. An insulation layer may advantageously be formed between the end ofthe main charge 2 and the throttle ring 7. The throttle ring 7 has aplurality of circumferentially spaced ports or openings 9 which permitsflow from the interior I of the solid charge :2 through the ports 9, theopenings 10a of the screen 10, and out the outlet 12.

The throttle ring 7 has a mean diameter d which is equal to, or aboutequal to, the mean diameter D of the main charge 2. Insulation of theend of the hollow charge 2 adjacent the rocket ring prevents combustionor wearing away of the ring at this location, and ensures that thethrottling effect will be maintained. The housing 6 defines an annularflow space 11 between the screen or flange 10 and the outer portion ofthe housing 6. This annular space 11 communicates with the outlet 12.

The method of operation of the device is as follows:

The detonator cap 5 is ignited and the ignition jet penetrates throughthe interior I of the solid charge 2 and impinges on the priming charge4 which is thus ignited. The ignition of the priming charge 4 as well asthe ignition of the entire length 15 of the interior of the solid charge2 causes the generation of gases. A portion of the priming charge gaseswill flow in the form of an inner current which will move upwardly inthe direction of the arrows designated Zi and another portion Za willflow upwardly in the annular passage 14. After ignition of wall 15,gases as indicated by the arrows Gi will flow upwardly from the burningof the charge 2 and, as indicated by the arrows Ga around the bottom endof charge 2 and upwardly along the side wall 16. Because of thethrottling effect produced by the ring 7 only a portion of the gaseswhich are generated during ignition and burning of the main charge 2will flow upwardly in the currents Zi and Gi, and pass through theopenings 9, the screen openings 10a and into the annular space 11 fordischarge through the outlet 12. A remaining portion will flow in thestreams Zn and Ga downwardly over the priming charge 4 and then upwardlythrough the passages defined in the holding device 3 in the passageway14 in order to contact the exterior wall 16 of the solid charge 2.

The throttle 7 thus insures that the gases which are formed initiallywithin the interior space J of the main charge 2 do not all flow throughthis end of the charge out the outlet 12, but that a portion of themflows around the exterior of the solid charge to maintain an ignitiontemperature along the exterior wall 16 during the combustion period.

As indicated in FIG. 2, a throttle ring 17 which is made of combustiblematerial may be employed instead of the ring 7 which is made of amaterial such as steel. In this instance, the entire surface of thethrottle ring 17 is covered with a noncombustible insulating coat '18 sothat it cannot be ignited by the inner partial gas current Zi and Giwhich will flow therearound. A combustible substance within the throttlering 17 is engaged by an ignition wire 19 which is insulated with anoncombustible fire retarding coat and it extends into the annular slot14. At the end of the ignition wire 15, there is arranged an ignitabletemperature feeler 20. When a temperature of the outer gas current G1which moves over the exterior wall of the main charge is attained whichwill ensure that the outer jacket or wall 16 will be ignited andmaintained burning, the temperature feeler 2 will ignite to set thecombustible substance in the throttle ring 17 afire and to cause theburning of the ring until it is completely consumed and no longerprovides a throttling effect on the main charge. This produces a directoutflow of all of the propellant gases produced by the combustion of themain charge 2 from both the interior and the exterior thereof. It isdesirable that the throttling effect be reduced as rapidly as possiblein order to avoid any unnecessary fiow losses around the annular slot14.

The flow screen 10 serves to retain any solid pieces which are detachedfrom the rocket composition 2 until they are completely burnt in orderto avoid that a device which is operated by the gases which aregenerated will not be adversely afiected. For example, a mechanicallysensitive gas turbine would be damaged by the carry over of large piecesof the main charge. In addition, the flow screen 10 ensures the loweringof the high temperature of the propellant gases by the heat withdrawaldown to an operating temperature admissible for a subsequent device suchas a turbine. In addition, soot and other impurities will be depositedon the screen to apply the cooling eifect which it produces.

What is claimed is:

1. A method of operating a thrust gas generator such as a rocket enginehaving a hollow substantially cylindrical charge arranged in acombustion chamber which has an outlet adjacent one end of the charge,comprising igniting the interior of the charge and throttling the interior of the end of the charge adjacent the outlet of the combustionchamber while permitting at least a partial gas flow through theopposite end and around the opposite end of the charge past the exteriorwall thereof to ignite 6 and to aid in maintaining ignition of theexterior wall of the charge.

2. A method, according to claim 1, wherein the solid charge employed hasa relatively long combustion time, comprising throttling of the end ofthe charge adjacent the outlet of the combustion chamber only during theignition phase and initial stages of combustion of the charge.

3. A method, according to claim 1, wherein the throttling of the chargeat the end adjacent the outlet of the combustion chamber is elfectedonly during a predetermined period Which corresponds to the timerequired for igniting the exterior of the main charge.

4. A method, according to claim 1, wherein the throttling isprogressively reduced.

5. A device for generating gases such as thrust gases for a rocketengine comprising wall means defining a combustion chamber having anoutlet, a hollow tubular charge having a burnable interior and exteriorand being located within said combustion chamber and having a first endadjacent the combustion chamber outlet and an opposite second end, saidcharge being spaced inwardly from said wall means and defining anexterior flow passage around the exterior of said charge communicatingwith said second end, and throttle means at said first end located tothrottle the gas flow from the interior through said first end andthrough said outlet and producing at least a partial flow of gases fromthe interior of said charge around said second end and through saidexterior flow passage in contact with the exterior wall of said charge,and means for igniting the interior of said tubular charge.

6. A device, according to claim 5, wherein said throttle means includesa ring extending around the opened interior of said tubular charge andabutting against said first end, said ring having a plurality of flowports therethrough communicating on one side with the interior of saidtubular charge and on the opposite side with the outlet of saidcombustion chamber.

7. A device, according to claim 6, including a cover member forpositioning a detonation cap adjacent first end of said charge engagedwith said ring and holding said ring in position adjacent said first endof said charge, the mean diameter of said ring correspondingapproximately to the mean diameter of said hollow charge.

8. A device, according to claim 5, wherein said throttle means comprisesa consumable throttle member.

9. A device, according to claim 8, wherein said throttle member is madeof combustible material.

10. A combustion chamber construction comprising wall means defining aninterior combustion chamber having an outlet, a hollow tubular chargehaving a first end located adjacent the combustion chamber outlet and anopposite second end remote from the outlet, means mounting said tubularcharge within said combustion chamber at a location to define an annularflow passage around the exterior of said charge, means holding adetonation cap at a spaced location from said first end of said charge,a throttle ring disposed between said holding means and said first endof said charge and having at least one opening therethrough permittingflow from said first end of said interior of said charge into said ringand through the opening to said outlet, a priming charge arrangedadjacent said second end of said hollow charge, the throttle memberbeing such to ensure a partial flow of gases produced after ignitionfrom the interior of said hollow charge toward first end for passagethrough the opening of said throttle member to said outlet and also fromthe interior of said charge to said second end around the exterior wallof said charge for ignition of the exterior wall and flow outwardly tosaid outlet.

11. A device, according to claim 10, wherein said means for holding saidring adjacent said first end of said hollow charge includes a flangemember extending outwardly from said holding means and defining ascreen, said screen being located between said outlet and the flow 7passed from the openings of said ring and from around the exterior ofsaid hollow charge to said outlet.

12. A device, according to claim 11, wherein said hollow charge isinsulated from said ring.

13. A device, according to claim 10, wherein said throttle ring is madeof a combustible material, and on igniting wire extending into saidcombustible material and having a feeler portion which is ignitable uponreaching of a predetermined temperature and which is located within theannular passage around the exterior of said hollow charge.

14. A device, according to claim 10, including a detonation cap held bysaid means for holding said detonation cap and located in alignment withthe first end of said tubular charge but on the opposite side of saidthrottle ring.

15. A device, according to claim 14, wherein said holding means engagessaid ring and positions said ring adjacent the first end of said hollowcharge said holding means including a outwardly extending flangesurrounding said ring and located between the openings of said ring andsaid outlet.

16. A method of operating a thrust gas generator, such as a rocketengine, having a hollow substantially cylindrical charge arranged in acombustion chamber which has an outlet adjacent one end of the charge,comprising igniting the interior of the charge and throttling the end ofthe charge adjacent the outlet of the combustion chamber to produce atleast a partial gas flow through the opposite end and around theopposite end of the charge past the exterior wall thereof to ignite andto aid in maintaining ignition of the exterior wall of the charge, thethrottling being controlled in dependence on the temperature of thegases which are directed around the exterior of the main charge.

17. A method of operating a thrust gas generator such as a rocket enginehaving a hollow substantially cylindrical charge arranged in acombustion chamber which has an outlet adjacent one end of the charge,and wherein the throttling element is made of a combustible materialcomprising igniting the interior of the charge and throttling the end ofthe charge adjacent the outlet of the combustion chamber to produce atleast a partial gas fiow through the opposite end and around theopposite end of the charge past the exterior wall thereof to ignite andto aid in maintaining ignition of the exterior wall of the charge andigniting the combustible throttling material after the temperature ofthe exterior of the hollow charge has reached a predetermined amount soas to reduce and substantially eliminate the throttling effect thereof.

References Cited UNITED STATES PATENTS 2,489,953 11/ 1949 Burney 60242X2,937,493 5/1960 Adelman 6039.82EX 2,942,547 6/1960 Rabern et al 60256X2,952,972 9/1960 Kimmel et al. 60271X FOREIGN PATENTS 219,530 8/1958Australia 6039.82E 1,029,282 3/1953 France 60256 DOUGLAS HART, PrimaryExaminer U.S. Cl. X.R. 6039.82, 256

